1. Field of the Invention
The present invention relates to a projection type display apparatus having a micro mirror type display element.
In this specification, the term “micro mirror type display element” means an optical modulator in which a large number of square micro mirrors each having some μm side are arranged on a silicon substrate, inclination of the micro mirrors is changed utilizing electrostatic attraction, thereby controlling whether light from a light source should be reflected in a direction of a screen. This micro mirror type reflection element generally has the same function as that of an element called DMD that is a trade name of Texas Instruments Incorporated.
2. Description of the Background Art
Conventionally, as a projector for projecting a predetermined image on a screen under magnification through a projection lens, there is a known projection type display apparatus having a micro mirror type display element which is a reflection type optical modulator (see Japanese Patent Application Laid-open No. 2005-128370 for example). The projection type display apparatus described in Japanese Patent Application Laid-open No. 2005-128370 includes a projection lens barrel which holds a projection lens, and a main body to which an illumination optical system such as various lenses and mirrors, and a micro mirror type display element are fixed, and on which the projection lens barrel is mounted.
Generally, in the projection type display apparatus having the micro mirror type display element, a flange focal length is adjusted to prevent a resolution of a picture to be projected on a screen from being deteriorated. The flange focal length is a length between a reference surface of a projection lens barrel that is a mounting reference on a main body in a direction of an optical axis and a reflection surface of the micro mirror type display element. As an adjusting method of the flange focal length, Japanese Patent Application Laid-open No. 2005-128370 (see paragraphs 0038, 0039 and FIG. 3) proposes a method in which a spacer is disposed between the reference surface of the projection lens barrel and the main body. According to this adjusting method of the flange focal length, when the projection type display apparatus is assembled, the flange focal length is adjusted in each projection type display apparatus.
In a projection type display apparatus having a conventional micro mirror type display element, a projection lens having a predetermined focal length is held by the projection lens barrel as a standard lens, and if this projection lens barrel is mounted on a main body when the projection type display apparatus is assembled, the projection lens barrel is not interchanged thereafter unless special requirement such as damage of the projection lens comes about. That is, in the projection type display apparatus having the conventional micro mirror type display element, an option lens such as a wide converter which is a lens for reducing a focal length to widen an angle of view and a tele converter which is a lens to increase the focal length to obtain a telephotography effect is not used. Therefore, in a general projection type display apparatus having the micro mirror type display element, the projection lens barrel is not interchanged.
On the other hand, in recent years, projection type display apparatuses with which option lenses can be used for making it possible to change a projection length from the projection type display apparatus having the micro mirror type display element to the screen to enhance the ease of use of the projection type display apparatus are required in the market. To meet the requirement, for the projection type display apparatus having the micro mirror type display element, there is required a structure which makes it possible to interchange between a projection lens barrel whose flange focal length is adjusted when a standard projection lens is held and assembled and an option projection lens barrel.
When a projection lens barrel is interchanged in the projection type display apparatus having the micro mirror type display element to make it possible to use an option lens, however, there is a problem that a sufficient resolution of a picture projected on a screen can not be obtained due to variation on the side of the projection lens barrel caused by a precision error of parts of the option lens and the projection lens barrel itself or a mounting error of the option lens on the projection lens barrel, and variation on the side of the main body caused by a precision error of parts of the micro mirror type display element and the main body itself and a mounting error of the micro mirror type display element on the main body. Japanese Patent Application Laid-open No. 2005-128370 does not propose concrete means for solving such a problem caused when the projection lens barrel is interchanged.